An image processing device is known, which performs multi-gradation recording by using a dither pattern in which each pixel of the image to print is composed of a block constituted by a plurality of dots.
In the dither process of converting image data to read-in print data, different dither patterns for cyan, magenta color and yellow color components, respectively, are utilized in the entire input image data. Inevitably, jaggy (zigzag) parts may be generated near any edge of the print image.
A method is known, which can prevent degradation of the image quality which may result from the jaggy parts. In this method, the gravity center of the gradation value input for each dither pattern is calculated, and the dither pattern is switched to another for that gravity center. (Refer to Patent Document 1)
Also known is a method of extracting the edge information and then switching the process on the pixel of interest in accordance with the edge information. (Refer to Patent Document 2)